1. Field of the Invention
The invention disclosed relates to arc resistant electrical distribution equipment.
2. Discussion of the Related Art
Circuit breakers used in switchgear cabinets are often constructed in a draw-out configuration that allows breaker insertion or removal by moving the breaker in a cradle assembly. The draw-out breakers have a connected position in which clusters, i.e. connectors having opposing stacks of plate-like fingers, engage bus bar extensions of bus bars in the switchgear cabinet. In a disconnected position, including the test position in some types of breakers, the clusters are disconnected from the bus bar extensions. To cover access to, and prevent inadvertent contact with, the bus bar extensions when the breaker is in the disconnected position, shutter systems have been utilized across a back plane of the cradle assembly. One shutter system includes sliding panels that protect all breaker phases at the same time. Another shutter system, taught in the copending International Application No. PCT/US2013/031345, filed Mar. 14, 2013, entitled “Independent Shutter System for Rack-In Breakers”, of common ownership herewith, includes a curtain having a pair of movable “hands” that are mounted to slide on a curtain mount, which, in turn, is mounted to slide on a pedestal that is mounted to a back-mold.
Circuit breakers are also used in motor control units, wherein the motor control unit may be inserted or removed from a motor control center (MCC) switchgear cabinet without shutting down all power to the cabinet. The motor control units have a connected position in which female connectors of the breakers are connected to respective bus bars, and a disconnected position in which the female connectors are disconnected from the bus bars. To cover access to, and prevent inadvertent contact with, the bus bars when the motor control unit is in the disconnected position, a common shutter system has been utilized across all power phases supplying the motor control unit.
Both draw-out circuit breakers and motor control units may share the requirement of making and breaking connections with installed bus bars or bus bar extensions i.e. the incoming power conductors contained in the switchgear cabinet. The making and breaking of connections and the handling of heavy currents in the area of connection between control devices like circuit interrupters (breakers), makes this area of the cabinet particularly susceptible to arcing. An arc flash is the rapid release of energy due to an arcing fault between phases, neutral or ground contacts. The resulting arc flash has the potential to cause considerable damage, including arcing-induced erosion of the contacts and injury to operators. The temperature of an arc flash may be capable of vaporizing metal and sending a blast of plasma and molten metal in all directions with extreme force. Damage may be caused to the switchgear both by the explosion of the arc flash and by the heat radiating from the blast. It is important to minimize the potential for harm to equipment and people by containing and redirecting the arc energy out from the switchgear.